U.S. patent number 8,698,322 [Application Number 12/730,823] was granted by the patent office on 2014-04-15 for adhesive-bonded substrates in a multi-chip module.
This patent grant is currently assigned to Oracle International Corporation. The grantee listed for this patent is John E. Cunningham, Robert J. Drost, Ashok V. Krishnamoorthy. Invention is credited to John E. Cunningham, Robert J. Drost, Ashok V. Krishnamoorthy.
United States Patent |
8,698,322 |
Drost , et al. |
April 15, 2014 |
Adhesive-bonded substrates in a multi-chip module
Abstract
A multi-chip module (MCM) is described in which at least two
substrates are mechanically coupled by an adhesive layer that
maintains alignment and a zero (or near zero) spacing between
proximity connectors on surfaces of the substrates, thereby
facilitating high signal quality during proximity communication
between the substrates. In order to provide sufficient shear
strength, the adhesive layer has a thickness that is larger than
the spacing. This may be accomplished using one or more positive
and/or negative features on the substrates. For example, the
adhesive may be bonded to: one of the surfaces and an inner surface
of a channel that is recessed below the other surface; inner
surfaces of channels that are recessed below both of the surfaces;
or both of the surfaces. In this last case, the zero (or near zero)
spacing may be achieved by disposing proximity connectors on a mesa
that protrudes above at least one of the substrate surfaces.
Inventors: |
Drost; Robert J. (Los Altos,
CA), Krishnamoorthy; Ashok V. (San Diego, CA),
Cunningham; John E. (San Diego, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Drost; Robert J.
Krishnamoorthy; Ashok V.
Cunningham; John E. |
Los Altos
San Diego
San Diego |
CA
CA
CA |
US
US
US |
|
|
Assignee: |
Oracle International
Corporation (Redwood Shores, CA)
|
Family
ID: |
44655450 |
Appl.
No.: |
12/730,823 |
Filed: |
March 24, 2010 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20110233789 A1 |
Sep 29, 2011 |
|
Current U.S.
Class: |
257/777; 257/746;
257/778; 257/734; 438/31; 257/773; 438/108; 438/244;
257/E23.169 |
Current CPC
Class: |
H01L
23/48 (20130101); H01L 25/0657 (20130101); H01L
23/5389 (20130101); H01L 2225/06531 (20130101); H01L
2924/15153 (20130101); H01L 2224/16145 (20130101); H01L
2224/16225 (20130101); H01L 2225/06555 (20130101) |
Current International
Class: |
H01L
23/538 (20060101) |
Field of
Search: |
;257/777,734,746,773,778,E23.169 ;438/244,108,31 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Malsawma; Lex
Assistant Examiner: Zhu; Sheng
Attorney, Agent or Firm: Park, Vaughan, Fleming & Dowler
LLP Stupp; Steven E.
Claims
What is claimed is:
1. A multi-chip module (MCM), comprising: a first substrate having
a first surface, wherein a first set of proximity connectors are
disposed on the first surface; a second substrate having a second
surface that faces the first surface, wherein a second set of
proximity connectors are disposed on the second surface, wherein
the first set of proximity connectors and the second set of
proximity connectors are separated by a spacing, wherein the second
surface includes a channel that is defined by an opening in the
second substrate along the second surface, wherein the channel
comprises an inner surface that faces the first surface and is
recessed in the second substrate away from the second surface, and
wherein the channel extends to an edge of the second substrate that
is perpendicular to the second surface; and an adhesive,
mechanically coupled to the first substrate and the inner surface,
having a thickness that is larger than the spacing, thereby
maintaining alignment and providing shear strength in the MCM, the
adhesive configured so that at least the spacing between the first
and second surfaces in an area where the first and second sets of
proximity connectors are located is free of adhesive.
2. The MCM of claim 1, wherein the adhesive is one or more of, air
cured, thermally cured, pressure cured and optically cured.
3. The MCM of claim 1, wherein the channel extends to at least an
edge of the second substrate that is approximately perpendicular to
the second surface, thereby defining an opening in the edge into
which the adhesive is deposited during assembly of the MCM.
4. The MCM of claim 1, wherein the proximity communication includes
at least one of, electrical proximity communication, inductive
proximity communication, conductive proximity communication and
optical proximity communication.
5. The MCM of claim 1, wherein the first surface includes another
channel having another inner surface that is recessed below the
first surface; and wherein the adhesive is mechanically coupled to
the first substrate via the other inner surface.
6. The MCM of claim 1, wherein the channel is enclosed by only
three sides, wherein the three sides comprise the inner surface and
two sides perpendicular to the second surface.
7. The MCM of claim 1, wherein the first substrate comprises a
first semiconductive material and the second substrate comprises a
second semiconductive material.
8. The MCM of claim 1, wherein the first substrate comprises a
first semiconductor die and wherein the second substrate comprises
a second semiconductor die.
9. An MCM, comprising: a first substrate having a first surface,
wherein a first set of proximity connectors are disposed on the
first surface; a second substrate having a second surface that
faces the first surface, wherein a mesa having a third surface
protrudes above the second surface, wherein the mesa is between
edges of the second substrate that are perpendicular to the second
surface, wherein the mesa comprises at least one of a
semiconductive and an electrically insulating material, wherein a
second set of proximity connectors are disposed on the third
surface, and wherein the first set of proximity connectors and the
second set of proximity connectors are separated by a spacing; and
an adhesive, mechanically coupled to the first surface and the
second surface and bonded to the first surface and the second
surface, having a thickness that is larger than the spacing,
thereby maintaining alignment and providing shear strength in the
MCM, the adhesive configured so that at least the spacing between
the first and second surfaces in an area where the first and second
sets of proximity connectors are located is free of adhesive,
wherein the adhesive is not in contact with the mesa.
10. The MCM of claim 9, wherein the adhesive is one or more of, air
cured, thermally cured, pressure cured and optically cured.
11. The MCM of claim 9, wherein the spacing is less than 5
.mu.m.
12. The MCM of claim 9, wherein the thickness is greater than 5
.mu.m and less than 200 .mu.m.
13. The MCM of claim 9, wherein the proximity communication
includes one or more of, electrical proximity communication,
inductive proximity communication, conductive proximity
communication and optical proximity communication.
14. The MCM of claim 9, wherein the mesa has edges that are
perpendicular to the third surface, and wherein each edge for the
mesa is between the edges of the second substrate that are
perpendicular to the second surface.
15. The MCM of claim 9, wherein the mesa is an extension of the
second substrate, and wherein the second substrate comprises the at
least one of the semiconductive and the electrically insulating
material.
16. A system, comprising an MCM, wherein the MCM includes: a first
substrate having a first surface, wherein first proximity
connectors are disposed on the first surface; a second substrate
having a second surface that faces the first surface, wherein a
second set of proximity connectors are disposed on the second
surface, wherein the first set of proximity connectors and the
second set of proximity connectors are separated by a spacing,
wherein the second surface includes a channel that is defined by an
opening in the second substrate along the second surface, wherein
the channel comprises an inner surface that faces the first surface
and is recessed in the second substrate away from the second
surface, and wherein the channel extends to an edge of the second
substrate that is perpendicular to the second surface; and an
adhesive, mechanically coupled to the first substrate and the inner
surface, having a thickness that is larger than the spacing,
thereby maintaining alignment and providing shear strength in the
MCM, the adhesive configured so that at least the spacing between
the first and second surfaces in an area where the first and second
sets of proximity connectors are located is free of adhesive.
17. The system of claim 16, wherein the adhesive is one or more of
air cured, thermally cured, pressure cured and optically cured.
18. The system of claim 16, wherein the channel extends to at least
an edge of the second substrate that is approximately perpendicular
to the second surface, thereby defining an opening in the edge into
which the adhesive is deposited during assembly of the MCM.
19. The system of claim 16, wherein the proximity communication
includes one or more of electrical proximity communication,
inductive proximity communication, conductive proximity
communication and optical proximity communication.
20. The system of claim 16, wherein the first surface includes
another channel having another inner surface that is recessed below
the first surface; and wherein the adhesive is mechanically coupled
to the first substrate via the other inner surface.
Description
BACKGROUND
1. Field
The present disclosure generally relates to multi-chip modules
(MCMs) and techniques for fabricating MCMs. More specifically, the
present disclosure relates to an MCM that includes substrates that
are bonded to each other using an adhesive.
2. Related Art
Multi-chip modules (MCMs) are being developed to facilitate
proximity communication (such as capacitively coupled
communication) between multiple integrated circuits (ICs) for the
next generation of high-performance computers. In these MCMs,
adjacent chips are often positioned face-to-face so that
information can be communicated between proximity connectors (such
as metal pads) on surfaces of facing chips. To facilitate ultrafast
chip-to-chip communications via capacitive coupling between the
proximity connectors, these chips need to be accurately positioned
so that the proximity connectors are horizontally aligned on a
micrometer scale, with a gap or spacing of a few microns or less
between the proximity connectors on the facing chips.
A simple and elegant technique for assembling the chips in an MCM
involves the use of an adhesive to bond the chips together to
maintain the desired horizontal and vertical alignment between the
proximity connectors. However, there is a tradeoff between the
strength of the adhesive layer between a pair of chips and the
signal quality during proximity communication. In particular, if
the adhesive layer or bondline is thick (e.g., a thickness of 10
.mu.m or more), the adhesive layer is ductile, but this increases
the spacing between the proximity connectors, which significantly
decreases the signal coupling and the signal quality.
Alternatively, if a thin adhesive layer is used, the signal
coupling and signal quality are improved, but the adhesive layer is
susceptible to shearing failure under lateral stress and strain,
which decreases the reliability of the MCM.
Hence, what is needed are an MCM and an associated fabrication
technique that do not suffer from the above-described problems.
SUMMARY
One embodiment of the present disclosure provides a multi-chip
module (MCM) that includes: a first substrate having a first
surface, where first proximity connectors are disposed on the first
surface; and a second substrate having a second surface that faces
the first surface, where second proximity connectors are disposed
on the second surface. The first proximity connectors and the
second proximity connectors are separated by a spacing, and the
second surface includes a channel having an inner surface that is
recessed below the second surface. Furthermore, an adhesive, which
is mechanically coupled to the first substrate and the inner
surface, and which has a thickness that is larger than the spacing,
maintains alignment and provides shear strength in the MCM, thereby
facilitating proximity communication of signals between the first
proximity connectors and the second proximity connectors.
This adhesive may be air cured, thermally cured, pressure cured or
optically cured. For example, the adhesive may include epoxy
glue.
Moreover, the channel may extend to at least an edge of the second
substrate that is approximately perpendicular to the second
surface, thereby defining an opening in the edge into which the
adhesive is deposited during assembly of the MCM. In some
embodiments, the first surface includes another channel having
another inner surface that is recessed below the first surface, and
the adhesive may be mechanically coupled to the first substrate via
the other inner surface.
In some embodiments, the spacing is less than 5 .mu.m. Furthermore,
the thickness may be greater than 5 .mu.m and/or may be less than
200 .mu.m.
Note that the proximity communication may include: electrical
proximity communication, inductive proximity communication,
conductive proximity communication, and/or optical proximity
communication.
In another embodiment of the MCM, in addition to or instead of the
channel, the second surface includes a mesa having a third surface
that protrudes above the second surface, and the second proximity
connectors are disposed on the third surface. In this embodiment,
the adhesive is mechanically coupled to the first surface and the
second surface.
Another embodiment provides a system that includes the MCM.
Another embodiment provides a method for fabricating the MCM.
During the method, the first surface and the second surface are
mechanically coupled using the adhesive.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a block diagram illustrating a multi-chip module (MCM) in
accordance with an embodiment of the present disclosure.
FIG. 2 is a block diagram illustrating a top view of a substrate
having a channel in accordance with an embodiment of the present
disclosure.
FIG. 3 is a block diagram illustrating an MCM in accordance with an
embodiment of the present disclosure.
FIG. 4 is a block diagram illustrating an MCM in accordance with an
embodiment of the present disclosure.
FIG. 5 is a block diagram illustrating an MCM in accordance with an
embodiment of the present disclosure.
FIG. 6 is a block diagram illustrating a system in accordance with
an embodiment of the present disclosure.
FIG. 7 is a flow chart illustrating a process for fabricating an
MCM in accordance with an embodiment of the present disclosure.
Note that like reference numerals refer to corresponding parts
throughout the drawings. Moreover, multiple instances of the same
type of part are designated by a common prefix separated from an
instance number by a dash.
DETAILED DESCRIPTION
Embodiments of a multi-chip module (MCM), a system that includes
the MCM, and a technique for fabricating the MCM are described.
This MCM includes at least two substrates that are mechanically
coupled by an adhesive layer that maintains alignment and a zero
(or near zero) spacing between proximity connectors on surfaces of
the substrates, thereby facilitating high signal quality during
proximity communication between the substrates. In order to provide
sufficient shear strength, the adhesive layer has a thickness that
is larger than the spacing. This may be accomplished using one or
more positive and/or negative features on the substrates. For
example, the adhesive may be bonded to: one of the surfaces and an
inner surface of a channel that is recessed below the other
surface; inner surfaces of channels that are recessed below both of
the surfaces; or both of the surfaces. In this last case, the zero
(or near zero) spacing may be achieved by disposing proximity
connectors on a mesa that protrudes above at least one of the
substrate surfaces.
By maintaining the alignment, and providing a zero (or near zero)
spacing and sufficient shear strength, this fabrication technique
may provide a reliable MCM with high signal quality. Furthermore,
the fabrication technique may be compatible with high-volume
manufacturing. For example, the channel(s) and/or the mesa may be
fabricated on the surfaces using semiconductor-process techniques,
and the resulting substrates may be assembled in the MCM using
low-cost, high-yield pick-and-place assembly equipment.
Consequently, the fabrication technique may reduce the cost and
complexity of the MCM.
We now describe embodiments of the MCM. FIG. 1 presents a block
diagram illustrating an MCM 100 that includes: a substrate 110
having a surface 112, where proximity connectors 114 are disposed
on surface 112; and a substrate 116 having a surface 118 that faces
surface 112, where proximity connectors 120 are disposed on surface
118. Note that proximity connectors 114 and proximity connectors
120 are separated by a spacing 122, and surface 118 includes at
least one channel, such as channel 124-1 (which may be an etch pit,
and more generally a negative feature), having an inner surface
(such as inner surface 126-1) that is recessed below surface 118.
Furthermore, an adhesive 128, which is mechanically coupled to
substrate 110 and one or more inner surfaces (such as inner surface
126-1), has a bondline thickness 130 that is larger than spacing
122, maintains alignment and provides shear strength in MCM 100,
thereby facilitating proximity communication with high signal
integrity between proximity connectors 114 and proximity connectors
120.
Note that the configuration in MCM 100 decouples spacing 122 and
thickness 130. For example, spacing 122 may be between 0-5 .mu.m,
while thickness 130 may be between 5-200 .mu.m. Thus, the depth of
a channel (such as channel 124-1) may increase bondline thickness
130 in MCM 100 by up to 40.times., while leaving spacing 122
unchanged.
A wide variety of adhesives may be used to mechanically couple
substrate 110 and substrate 116. For example, adhesive 128 may
include epoxy glue or a silicon-based adhesive. Moreover, adhesive
128 may be: air cured, thermally cured, pressure cured and/or
optically cured (for example, using ultra-violet light).
Wicking of adhesive 128 into a channel (such as channel 124-1) and
thickness 130 may be determined by: the adhesive viscosity, the
surface tension of adhesive 128, and the pressure applied to
external surfaces 132 of substrates 110 and 116 during assembly.
For example, the viscosity may be 200 cps.
As shown in FIG. 2, which presents a block diagram illustrating a
top view of substrate 116, to facilitate assembly of MCM 100, the
one or more channels (such as channel 124-1) in substrate 116,
which capture and guide adhesive 128, may extend to at least an
edge 210 of substrate 116 that is approximately perpendicular to
surface 118, thereby defining one or more openings (such as opening
212-1) in edge 210 into which adhesive 128 is deposited during
assembly of MCM 100. For example, surfaces 112 and 118 of
substrates 110 and 116 may be aligned and pressed together to
achieve a desired spacing 122. Then, adhesive 128 may be injected
into openings 212, and subsequently cured to bond substrates 110
and 116 to each other. Note that this single process operation is
compatible with existing fabrication techniques and, thus, may
facilitate low-cost, high-yield fabrication of MCM 100.
While MCM 100 illustrates the use of a single channel (such as
channel 124-1) in each adhesive bondline, a variety of
configurations that include positive and/or negative features may
be used to decouple spacing 122 and thickness 130. For example, as
shown in FIG. 3, which presents a block diagram illustrating an MCM
300, surface 112 may also include one or more channels (such as
channel 124-3) having inner surfaces (such as inner surface 126-3)
that are recessed below surface 112. In this embodiment, adhesive
128 is mechanically coupled to inner surfaces in a pair of channels
(such as channels 124-1 and 124-3), which may double thickness 310
relative to thickness 130 in FIG. 1.
Alternatively or additionally, a positive feature may be used to
decouple spacing 122 and thickness 130. For example, as shown in
FIG. 4, which presents a block diagram illustrating an MCM 400, a
mesa 410 having a surface 412 may protrude a height 414 above
surface 118, where proximity connectors 120 are disposed on surface
412. In this embodiment, adhesive 128 mechanically couples surface
112 and surface 118, while height 414 ensures that spacing 122 is
less than thickness 130.
In some embodiments, the substrates in the MCM include island chips
(such as processors) and bridge chips, which couple signals between
island chips. For example, as shown in FIG. 5, which presents a
block diagram illustrating an MCM 500, the island chips may be
face-down and a bridge chip may be placed face-up. (Alternatively,
in a flip-chip configuration the island chips may be face-up and
the bridge chip may be face-down.) Note that the island and bridge
chips receive signals, power and ground from the package substrate
through C4 solder and/or copper pillars as level-one interconnects,
and that the bridge chip communicates with the island chips using
proximity communication. Moreover, in addition to maintaining the
alignment of the proximity connectors (not shown) between the
island chips and the bridge chip, the adhesive may keep the island
chip from falling down (i.e., it may keep the spacing between the
proximity connectors on the adjacent chips small). Thus, given a
thickness h2 of the bridge chip, the adhesive may help maintain the
mechanical clearances, h1 and h3, between the components in MCM
500.
One or more of the preceding embodiments of the MCM may be included
in a system and/or an electronic device. This is shown in FIG. 6,
which presents a block diagram illustrating a system 600 that
includes MCM 610. In general, an MCM may include an array of chip
modules (CMs) or single-chip modules (SCMs), and a given SCM may
include at least one substrate, such as a semiconductor die. Note
that an MCM is sometimes referred to as a `macro-chip.`
Furthermore, the substrate may communicate with other substrates,
CMs and/or SCMs in the MCM using proximity communication of
electromagnetically coupled signals (which is referred to as
`electromagnetic proximity communication`). For example, the
proximity communication may include: communication of capacitively
coupled signals (`electrical proximity communication`) and/or
communication of optical signals (such as `optical proximity
communication`). In some embodiments, the electromagnetic proximity
communication includes inductively coupled signals and/or
conductively coupled signals.
Furthermore, embodiments of the MCM may be used in a variety of
applications, including: VLSI circuits, communication systems (such
as in wavelength division multiplexing), storage area networks,
data centers, networks (such as local area networks), and/or
computer systems (such as multiple-core processor computer
systems). For example, the MCM may be included in a backplane that
is coupled to multiple processor blades, or the MCM may couple
different types of components (such as processors, memory,
input/output devices, and/or peripheral devices). In some
embodiments, the MCM performs the functions of: a switch, a hub, a
bridge, and/or a router.
Note that system 600 may include, but is not limited to: a server,
a laptop computer, a communication device or system, a personal
computer, a work station, a mainframe computer, a blade, an
enterprise computer, a data center, a portable-computing device, a
supercomputer, a network-attached-storage (NAS) system, a
storage-area-network (SAN) system, and/or another electronic
computing device. Moreover, note that a given computer system may
be at one location or may be distributed over multiple,
geographically dispersed locations.
MCMs in FIGS. 1 and 3-5 and/or system 600 in FIG. 6 may include
fewer components or additional components. For example, a given MCM
may include one or more negative features (such as channels 124 in
FIGS. 1 and 3) and/or one or more positive features (such as mesa
410 in FIG. 4). Moreover, in some embodiments channels 124 in FIGS.
1-3 may not extend to the edges of the substrates (for example,
they may be rectangular or square etch pits). Furthermore, a
negative feature may be defined in one or more layers that are
deposited on a surface of a substrate, and the negative features
may be recessed below a surface of the top layer deposited on the
substrate. Similarly, a positive feature may protrude above a local
surface, which may be the same as or different from a top layer
deposited on the substrate. Thus, in the preceding embodiments a
surface of a substrate should be understood to include a surface of
a layer deposited on the substrate or a surface of the substrate
itself.
Note that a given positive or negative feature may be fabricated
using an additive process (in which material is deposited or added
to a substrate) or a subtractive process (in which material is
removed from a substrate). For example, the process may include:
plating, sputtering, isotropic etching, anisotropic etching, a
photolithographic technique and/or a direct-write technique.
Furthermore, these features may be fabricated using a wide variety
of materials (such as: a semiconductor, metal, glass, sapphire,
and/or silicon dioxide) and/or may have a wide variety of shapes
(such as a groove, a trapezoid, a rectangular shape, a half
hemisphere, etc.).
Although these embodiments are illustrated as having a number of
discrete items, the MCM and the system are intended to be
functional descriptions of the various features that may be present
rather than structural schematics of the embodiments described
herein. Consequently, in these embodiments two or more components
may be combined into a single component, and/or a position of one
or more components may be changed.
We now describe embodiments of a process. FIG. 7 presents a flow
chart illustrating a process 700 for fabricating an MCM. During the
process, an adhesive is deposited in or proximate to a positive or
negative feature on one or two substrates in the MCM (operation
710), where the positive or negative feature ensures that a
thickness of the adhesive is decoupled from a spacing of proximity
connectors on the two substrates. Then, the adhesive is cured
(operation 712), thereby maintaining the spacing and alignment of
the proximity connectors on the two substrates.
In some embodiments of process 700, there are additional or fewer
operations. Moreover, the order of the operations may be changed,
and/or two or more operations may be combined into a single
operation.
The foregoing description is intended to enable any person skilled
in the art to make and use the disclosure, and is provided in the
context of a particular application and its requirements. Moreover,
the foregoing descriptions of embodiments of the present disclosure
have been presented for purposes of illustration and description
only. They are not intended to be exhaustive or to limit the
present disclosure to the forms disclosed. Accordingly, many
modifications and variations will be apparent to practitioners
skilled in the art, and the general principles defined herein may
be applied to other embodiments and applications without departing
from the spirit and scope of the present disclosure. Additionally,
the discussion of the preceding embodiments is not intended to
limit the present disclosure. Thus, the present disclosure is not
intended to be limited to the embodiments shown, but is to be
accorded the widest scope consistent with the principles and
features disclosed herein.
* * * * *